1. Field of the Invention
The present invention relates to a process for producing hydrogen cyanide by using formamide as a starting raw material.
Hydrogen cyanide is an indispensable basal chemical to be used as various starting raw materials for organic synthesis of mainly methacrylic ester, lactic acid and the like and also to be used in mining and metallurgical industries. In addition, it has recently expanded the demand as the starting raw materials for the synthesis of pharmaceuticals and agrichemicals and the like.
2. Description of Related Arts
As a process for industrially producing hydrogen cyanide, there are spread the thermal cracking of formamide, the oxidation of methane along with ammonia and a like process. Hydrogen cyanide is also mass-produced as the byproduct in the process for producing acrylonitrile by the oxidation of propylene along with ammonia.
The production of hydrogen cyanide by the thermal cracking of formamide is represented by the reaction equation (1) in which hydrogen cyanide and water each in one (1) mol are produced from one (1) mol of formamide, EQU HCONH.sub.2 .fwdarw.HCN+H.sub.2 O (1)
which reaction is accompanied by the reaction equation (2) in which the formamide is decomposed into ammonia and carbon monoxide. EQU HCONH.sub.2 .fwdarw.NH.sub.3 +CO (2)
In order to efficiently produce hydrogen cyanide from formamide, it is indispensable to rapidly force the reaction as represented by the equation (1) and at the same time to suppress the reaction represented by the equation (2) as much as possible. Accordingly, attempts have heretofore been made to research and develop a catalyst enhanced in activity and selectivity for the reaction represented by the equation (1).
There are described, for example, in U.S. Pat. No. 2,086,507 that a fused manganese oxide is effective as a catalyst in the production of hydrogen cyanide from formamide and in U.S. Pat. No. 2,534,000, a process for producing hydrogen cyanide in high selectivity by using a manganese oxide as a catalyst and by efficiently evaporating formamide under vacuum.
However, these catalysts that have heretofore been employed involve the problem that in spite of their high activity the selectivity to the objective hydrogen cyanide is not so high and ammonia is by-produced in an amount of about 10%.
The by-production of ammonia not only lowers the yield of the objective hydrogen cyanide but also functions to accelerate the polymerization of hydrogen cyanide in the form of liquid. Thus, in the case of isolating the produced hydrogen cyanide, the by-produced ammonia must be removed by washing in advance, the reaction gas with sulfuric acid or the like. The ammonia sulfate which is produced from sulfuric acid and ammonia is discharged as a byproduct in a large amount from some chemical industries, but is not so hailed as before as the fertilizer because of the soil being acidified by the use thereof. With the enhanced environmental protection motion, the problem with the treatment of the ammonium sulfate has recently been materialized. As mentioned hereinbefore, the by-production of ammonia gives rise to an increase in the production cost of hydrogen cyanide as well as the problem the treatment of ammonium sulfate. Under such circumstances, it is eagerly desired to develop a catalyst capable of producing hydrogen cyanide in high selectivity by suppressing the by-production of ammonia and carbon monoxide.